There's room for speculation there, I guess. McCoy was said to be "home, resting comfortably, pumped full of tranquilizers" a few scenes earlier. So unless he lived in that giant space city, he must have gotten away from it for a while at least - but returning there is by no means out of the question. The bar might be aboard Spacedock Earth, or down at San Francisco, or perhaps in Berlin, or on the Moon, or at the bottom of the Caribbean. Travel around and out of the globe in the 23rd century is fairly trivial, at least if you are a Starfleet officer...